Saul's eldest son and heir, and David's sworn friend — the crown prince who took his father's rival's side. He wins a reckless victory at Michmash with only his armor-bearer (1 Samuel 14), and when he meets David he 'cuts a covenant' with him and gives him his own robe, sword, bow and belt (18:1-4) — in effect handing over the insignia of the succession. ⚠️ He twice warns David of Saul's plots and argues for him to his father's face, and their last meeting ends with an oath binding their descendants (20:16-17; 23:18) — an oath David keeps years later by seeking out Jonathan's crippled son Mephibosheth and seating him at the king's table (2 Samuel 9). He dies beside his father on Gilboa, and David's lament for him is the most personal poetry in the books of Samuel.